Published French patent application No. 2 477 128 filed Feb. 29, 1980 describes a cation conductive vitreous compound having a formula: aP.sub.2 S.sub.5, bLi.sub.2 S, cLiX, where X stands for chlorine, bromine or iodine, and a, b, and c are numbers chosen in such a manner that b/(a+b) lies in the range 0.61 to 0.70 and c/(a+b+c) is less than or equal to the maximum solubility in the vitreous phase of LiX in the compound aP.sub.2 S.sub.5, bLi.sub.2 S.
The present invention relates to electrochemical cells of the above type having a lithium based negative active material and an electrolyte made of said vitreous compound.
Preferred embodiments of the invention provide cells of this type having high energy density by virtue of a suitable choice of positive active material.